Photocouplers (including photorelays) can convert an input electrical signal into an optical signal by using a light emitting element, receive light using a light receiving element, and then output an electrical signal. Hence, the photocouplers can transmit electrical signals in a state where the input and output leads are insulated from each other.
In industrial equipment, office equipment, and household appliances, different power supply systems such as a DC voltage system, an AC power supply system, a telephone line system, and a control system are disposed inside one device. However, if different power supply systems and circuit systems are directly coupled, operation errors may occur.
In this case, normal operation can be maintained by using photocouplers because the different power supplies are insulated from each other.
For example, many photocouplers are used in an inverter air conditioners etc. for a load that may include an alternatin current load. In the case where photocouplers are used for signal switching in an integrated circuit tester application, an extremely large number of photocouplers mounted; and it is extremely desirable to reduce the photocoupler size due to the need to reduce the mounting surface area on the substrate.